The present invention is directed to a pressurized gas dispensing system. More particularly, the present invention is directed to a method and apparatus useful for transferring a gas from a refueling station into one or more storage tanks.
Because of the interrelationship between the temperature, pressure and density of gases, the amount of hydrogen, H2, (or compressed natural gas (CNG)) that can safely be introduced into a storage tank, such as a vehicle storage tank, during refueling necessarily depends upon factors such as the volume, design pressure, and temperature of the tank, and the temperature and pressure of the gas inside the tank. Industry convention sets the pressure rating for H2 fuel tanks at the standard temperature of 15 degrees Celsius, so nominal pressure ratings such as 250 bar, 350 bar, 500 bar and 700 bar, correspond to an internal gas temperature of 15 degrees Celsius. During rapid refueling, the internal tank temperature will typically rise about 50 degrees Celsius due to adiabatic compression of the gas and the reverse Joule-Thompson effect. After the tank is filled, the temperature and pressure inside the tank will decrease as the gas cools. Wide variations in ambient temperature above or below the standard condition of 15 degrees Celsius can also have a significant effect on the indicated pressure inside the tank during and after refueling.
Prior art refueling systems have used various devices and methods for regulating the cutoff pressure and for determining the amount of gas dispensed when refilling vehicle storage tanks. For example, U.S. Pat. No. 3,837,377 (McJones) discloses a means for sensing the pressure of a given amount of reference gas contained in a closed, reference pressure vessel that is in thermal contact with the tank being filled. Gas is charged into the tank and the pressure in both the reference vessel and the tank are monitored and compared. Refueling is terminated whenever there is a predetermined pressure differential between the gases in the reference vessel and the tank. The use of an internal reference vessel increases fabrication and installation costs and also presents an ongoing maintenance problem with regard to checking the integrity of the reference vessel. If the reference vessel leaks, there is no way to verify that the reference pressure is correct and has not changed. Also, the use of a reference vessel as disclosed in U.S. Pat. No. 3,837,377 (McJones) will not provide a desirably quick response time in that the gas flow rate will be gradually lowered as the receiving tank pressure begins to approach the reference pressure.
U.S. Pat. No. 4,527,600 (Fisher et al.) discloses a CNG dispensing system comprising a relatively high pressure storage tank from which CNG flows through a control valve, pressure regulator and flow sensing transducer to the tank being filled. Temperature and pressure transducers in the storage tank transmit electric signals to a process control electronic control that calculates the volume of gas dispensed by comparing the initial and final values of the CNG inside the storage tank. A differential pressure cell communicating with the storage tank and with the vehicle tank fill line generates a signal that is used by the electronic control to operate a solenoid-controlled valve disposed in the fill line. Flow continues until pressure in the vehicle storage tank reaches a preselected set point, causing the regulator to close. The regulator set point is not, however, adjusted according to the temperature inside the vehicle tank.
U.S. Pat. No. 5,029,622 (Mutter) discloses a gas refueling device and method of operation wherein at least one temperature sensor is utilized for sensing the temperature of ambient air external to the refueling device. An advantage of this refueling device is disclosed to be that set/actual value comparisons between pressures and temperatures are carried out at short time intervals, with the permissible set values corrected according to the development of the preceding measurements. Here again, however, the temperature inside the vehicle storage tank is not monitored during refueling.
U.S. Pat. No. 4,966,206 (Bauman et al.) discloses another device for refilling tanks with CNG that automatically adjusts the filling pressure of the gaseous fuel to the local ambient temperature. A temperature sensor is disposed outside the casing of the device for generating a signal in response to ambient temperature. A pressure sensor is connected to the suction line of the compressor for generating a signal in response to the gas inlet pressure. A pressure difference sensor is also provided for generating a signal in response to a difference in pressure between the fuel pressure in the inlet line of the casing and the pressure inside the casing. A control device disposed in the casing is connected to each of the three sensors in order to receive signals from each. This control device is also connected to the inlet valve and discharge valve in order to control the inlet valve and discharge valve in response to the signals received from the sensors.
U.S. Pat. No. 5,238,030 (Miller et al.) discloses a pressurized fluid dispensing system that can automatically compensate for non-standard ambient gas temperature to promote complete filling of a pressurized storage tank. Pressure and temperature transducers connected to a supply plenum measure the stagnation pressure and temperature of the CNG, and a pressure transducer in fluid communication with the vehicle tank via the dispensing hose assembly is used to determine the pressure in the vehicle tank. A second temperature transducer is used to measure the ambient temperature. An electronic control system connected to the pressure and temperature transducers and to the control valve assembly calculates a vehicle tank cut-off pressure based on the ambient temperature and on the pressure rating of the vehicle tank that has been preprogramed into the electronic control system and automatically turns off the CNG flow when the pressure in the vehicle tank reaches the calculated cut-off pressure. U.S. Pat. No. 5,259,424 (Miller et al.), which is related to U.S. Pat. No. 5,238,030 (Miller et al.), discloses a similar system in which the pressure transducer is used to determine the discharge pressure. An electronic control system calculates the volume of the vehicle tank and the additional mass of CNG required to increase the tank pressure to the cut-off pressure. The CNG flow is turned off when the additional mass has been dispensed into the vehicle tank.
U.S. Pat No. 5,628,349 (Diggins) discloses a system for dispensing pressurized gas in which temperature inside a receiving tank is monitored and is used by a computer to adjust fill pressure to compensate for temperature and pressure rise attributable to adiabatic compression of gas inside the receiving tank. The system here uses the pressure and temperature of the receiving tank to calculate gas volume inside the tank. Actual tank pressure and gas volume are compared to an estimated tank finish pressure and corresponding gas volume for the tank.
Several other patents include are cited herein for background information only. These include the following. U.S. Pat. No. 4,515,516 (Perrine et al.) discloses a method and apparatus for compressing gases. The compressor used here is suited for filling a natural gas storage tank in a vehicle over an extended period of several hours. An auxiliary storage tank is used for fast filling. U.S. Pat. No. 4,984,457 (Morris) discloses a tank gauging apparatus and method for gauging the amount of liquid in a container of liquid and gas under flow or zero gravity conditions. U.S. Pat. No. 5,156,198 (Hall) discloses a fuel pump lock and dispensing system wherein data from a vehicle computer is used to identify the vehicle, transfer data to and from the vehicle computer to a fuel pump computer, and to unlock the fuel pump. U.S. Pat. No. 5,169,295 (Stogner et al.) discloses a method and apparatus for compressing gas where two accumulators are alternately filled with gas from a gas supply and the gas is forced out of one end of each of the accumulators into a gas-receiving conduit by liquid forced into the other end of each of the accumulators. U.S. Pat. No. 5,454,408 (DiBella et al.) discloses a variable volume CNG storage vessel connected to a line supplying pressurized natural gas. The vessel connects to a dispensing station fitting. When a tank is being filled, a controller responds to pressure within the storage vessel to vary the volume of the storage vessel.
A system for dispensing pressurized gas is provided which includes a pressurized gas source, a receiving tank, a sealed gas flow line connected between the gas source and the receiving tank, a valve in the gas flow line for initiating and terminating flow of the pressurized gas between the gas source and the receiving tank operable by a valve signal, and an electronic controller. A temperature sensor is also included for sensing temperature of a gas inside the receiving tank which includes a temperature signal generator for generating a temperature signal corresponding to the temperature of the pressurized gas in the receiving tank. The temperature signal is used by the electronic controller. Likewise, a pressure sensor for sensing pressure of a gas inside the receiving tank is included which includes a pressure signal generator for generating a pressure signal corresponding to the pressure of the gas inside the receiving tank. The pressure signal is also used by the electronic controller. The electronic controller stores a tank rated density and the temperature and pressure signals. The electronic controller also periodically calculates density of the gas in the receiving tank based on the temperature and pressure signals. The electronic controller compares the density of the gas in the receiving tank with the tank rated density and initiates flow of pressurized gas through the valve by generating a valve signal when the density of gas in the receiving tank is below the tank rated density and terminates flow of pressurized gas through the valve by generating a valve signal when the density of the gas in the receiving tank reaches the tank rated density.
Preferably, the pressurized gas is hydrogen gas. Preferably, the electronic controller generates a percent full signal, where the percent full signal is the ratio of the density of gas in the receiving tank to the tank rated density.
A refrigeration system for cooling the gas exiting the pressurized gas source prior to the gas entering the receiving tank may also be included. Here, the refrigeration system may use a mechanical refrigeration cycle, for example, using a hydrofluorocarbon. Alternatively, the refrigeration system may include a liquid hydrogen source and a cold storage device, wherein the cold storage device is cooled by hydrogen from the liquid hydrogen source and the refrigeration system also includes a heat exchanger adapted to receive and cool gas exiting the pressurized gas source prior to its flowing to the receiving tank. The cold storage device may use a condensable refrigerant to store the refrigeration until cooling is needed when filling the receiving tank. Again, the refrigerant may be a hydrofluorocarbon. The cold storage device may also use a compressed gas such as argon or nitrogen. The refrigeration system may include a refrigerated container that at least partially surrounds the pressurized gas source.
Finally, the electronic controller may calculate the density of the gas in the receiving tank based on estimates of the temperature and pressure signals.
A method for dispensing pressurized gas is also provided which includes the steps of providing a pressurized gas source, a receiving tank, a sealed gas flow line connected between the gas source and the receiving tank, and a valve in the gas flow line for initiating and terminating flow of the pressurized gas between the gas source and the receiving tank operable by a valve signal. The method also includes the step of providing an electronic controller, a temperature sensor for sensing temperature of a gas inside the receiving tank, and a pressure sensor for sensing pressure of a gas inside the receiving tank. The temperature sensor includes a signal generator for generating a temperature signal corresponding to the temperature of the pressurized gas in the receiving tank. The temperature signal is adapted to be received by the electronic controller. The pressure sensor also includes a signal generator for generating a pressure signal corresponding to the pressure of the gas inside the receiving tank. The pressure signal is adapted to be received by the electronic controller. The method further includes the steps of storing a tank rated density and pressure signals in the electronic controller, periodically calculating a density of the gas in the receiving tank based on the temperature and pressure signals, and periodically comparing the density of the gas in the receiving tank with the tank rated density. Flow of pressurized gas through the valve is initiated by generating the valve signal when the density of gas in the receiving tank is below the rated density, and flow of pressurized gas through the valve is terminated by generating the valve signal when the density of the gas in the receiving tank reaches the rated density. The method may further include the step of generating a percent full signal, wherein the percent full signal is the ratio of the density of gas in the receiving tank to the rated density. The method may further include the step of cooling the gas exiting the pressurized gas source prior to the gas entering the receiving tank using a refrigeration system. The step of cooling may include using a liquid hydrogen source. The step of calculating the density of the gas in the receiving tank may be based on estimated temperature and pressure signals. The step of calculating the density of the gas in the receiving tank may include obtaining temperature sensor and pressure sensor readings by calculating estimated values based on an estimate of density and flow of gas exiting the pressurized gas source.